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Re: [Gcl-devel] [Re: Executable memory: further programs that fail]

From: Camm Maguire
Subject: Re: [Gcl-devel] [Re: Executable memory: further programs that fail]
Date: 01 Dec 2003 17:47:19 -0500
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.2

Greetings!  Tim, the -Wa,--execstack option is trivial to implement
and is sure to work.  It would be nice to have a configure test to
determine when it is necessary, but all gcc I have available seem to
take the option.  Even though it is not the desirable long term option
as the poster states, a final solution must await a fix to emacs'
unexec, at which point we can move DBEGIN to an internal variable, and
test if holes are permitted in the heap.  So at this point I recommend
punting and disabling exec-shield until a work-around for unexec is at
hand.  Your thoughts?

Take care,

Tim Daly  <address@hidden> writes:

> Some hints from the Fedora Core mailing list about making programs 
> run under exec-shield.
> Tim
> From: Ingo Molnar <address@hidden>
> Subject: Re: Executable memory: further programs that fail
> To: Fedora Development <address@hidden>
> Date: Mon, 24 Nov 2003 05:42:27 -0500 (EST)
> On Sat, 22 Nov 2003, Gerard Milmeister wrote:
> > So is it alright to include in Fedora packages that require exec-shield
> > to be turned off? Should there be a wrapper-script that calls the main
> > executable with 'setarch'?
> all 'third party' apps will run with exec-shield disabled by default.
> _Iff_ a package is recompiled under Fedora (using Fedora's gcc and
> binutils) then you might end up with an app that has exec-shield enabled
> although the app itself for whatever reason has some executability
> assumption.
> In this case there are myriads of ways to make the app work again:
>  - use 'setarch i386 <app>' [or rather, use the 'i386 <app>' shortcut]
>  - add this gcc option to the CFLAGS in the Makefile:
>       -Wa,--execstack
>  - add the following oneliner anywhere in the app's source in an assembly
>    file to disable exec-shield:
>       .section .note.GNU-stack, "x", @progbits; .previous
>  - disable exec-shield globally, put "kernel.exec-shield = 0" into 
>    /etc/sysctl.conf.
>  - the preferred solution: fix the app itself to not assume executability
>    of non-executable regions or not hardcode any VM properties such as
>    'mmaps start at 2 GB'. Both assumptions are illegal and these apps will
>    likely break on 64-bit architectures too, so they should be fixed. Note
>    that typically the changes needed are quite simple.
> in any case, please keep reporting apps that need an executable stack, we
> want to track them all down and fix them for good. Fortunately 99.9% of
> the 5000+ binaries in a full Fedora Core 1 install work out of box.
> note that there are also prelink related problems, which we want to know
> about and fix just as much, but which should not be confused with
> exec-shield problems. Sometimes these do get mixed up.
> (in any case, please also read the extensive description provided by
> Roland McGrath's "exec-shield mmap & brk randomization" email.)
>       Ingo
> - --
> fedora-devel-list mailing list
> address@hidden
> http://www.redhat.com/mailman/listinfo/fedora-devel-list
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Camm Maguire                                            address@hidden
"The earth is but one country, and mankind its citizens."  --  Baha'u'llah

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